1. Field of the Invention
The invention relates to a sealing tape which is suitable for winding around pipe ends, preferably pipe threads, and for sealing threaded joints, screw fittings and pipe joints, which has a waterproof functional layer, preferably with one or more base layers, and the use thereof.
2. Discussion of Related Art
It is known that pipelines are joined together by means of pipe joints such as screw joints or spigot joints. Screw joints primarily occur in the form of threaded pipes or so-called fittings, which enable changes of direction in the pipe run, branching or the termination of threaded pipes or pipelines. Like the pipelines, these shaped parts can be manufactured from various materials and can take the form of tees, bends, crosses, sockets, reducing sockets or reducing nipples. The end of the piping or the pipe element is for example in the form of an external taper thread and the end of the screw fitting has an internal cylindrical thread.
In order to make the joints between the screw fittings and the piping strong and leakproof the thread flanks of the pipe end and the screw joint must be pressed firmly onto one another by means of a certain thread reach. For this reason it is necessary to wind a hemp bundle normally around the external thread of the pipe end, whereby the hemp bundle is laid axially along the thread reach starting from the end of the thread and then wound clockwise around the thread from the start of the thread. To make sure the hemp does not unwind again and that it is lubricious when the pipe fitting is screwed in, the hemp must be coated with a paste-type sealant, which is a lengthy process requiring exacting work.
After the screw fitting has been screwed onto the end of the pipe the protruding hemp is removed using a hand hacksaw. Here, however, there is a danger firstly, that the user will injure himself with the hand hacksaw due to fact that the paste-type sealant has made the surface slippery, and secondly, that the hemp will be pulled out of the turns of the thread by the saw blade.
Moreover, as it is a natural product hemp is subject to aging which reveals itself in the form of drying out and decaying. Although the aging process can be delayed by means of the sealant applied to the hemp, it is impossible to prevent it entirely, and thus there is a danger of screw pipe joints in time becoming leaky and therefore requiring continual checking.
Also touching hemp is an unpleasant sensation for the user, since it feels rough and scratchy. Moreover, skin contact with hemp has often been observed to give rise to irritations and even allergies.
In order to eliminate the above disadvantages, DE-PS 40 15 394 proposes a sealing tape which appears to be suitable for sealing threads in pipe installations, and in which small hemp fibers or hemp-like man-made fibers are bonded to polytetrafluoroethylene sheeting or embedded in the sheeting. Although this sealing tape delays the drying-out experienced by the hemp, it is evident that if the polytetrafluoroethylene sheeting is damaged by the pipe end being screwed in and out or is screwed along with it into the screw joints, there is a danger that the hemp fibers will still lose moisture, even if they now do so more slowly, and the substances in the pipelines such as water or gas will seep out due to the sealing tape becoming brittle. This process is encouraged still further if the piping system is subjected to large changes in temperature or continuously subjected to medium or high temperatures.
In addition it cannot be ignored that although the sealing tape coated with polytetrafluoroethylene is thermally stable, its heat stability is impaired due to the presence of hemp fibers in the sealing tape and permanent sealing is not guaranteed.
In order to make the screw joint reasonably leakproof, sealing tapes consisting of polytetrafluoroethylene also have to be wound around the external thread of the pipe element several times, a time-consuming process. It is evident here that the joint will become leaky even if the screw fitting becomes only slightly unscrewed. In the day-to-day work of a heating technician for example, it is often necessary to unscrew the fitting in order to correct the relative positions of the screw fitting and the pipe element and only by means of such adjustment can elbows in the heating installations of a building be adapted to the structure of the masonry.
Moreover, this state of the art completely overlooks the fact that in case of fires in the building or when piping or screw joints are reconditioned there is a danger that decomposition products containing fluorine, such as fluorophosgene, carbonyl fluoride, tetrafluoromethane, HF, hexafluoroethane, trifluoroacetylfluoride and perfluoroisobutene are produced, which in part are highly toxic. The long-term action of these decomposition products on humans causes so-called polymer fume fever and pulmonary edemas. Moreover, the decomposition products containing fluorine will hamper the work of fire fighters if a fire breaks out in the building.